A hydrocarbon-degrading bacterium Providencia rettgeri L1 was isolated from petroleum in Shengli oil field, China. The petroleum-degradation characteristics were investigated. The degradation rate of petroleum by the strain was 45.9% in petroleum-mineral medium (5 g/L) in 14 d measured by ultraviolet-visible spectrophotometer. The intracellular crude enzymes of Providencia rettgeri L1 were prepared and supplemented with formate dehydrogenase to construct an enzyme cocktail. The petroleum degradation rate of the cocktail reached 49.5% in 8 h, which was much faster than the strain. The subfraction saturates and aromatics in petroleum were analyzed by gas chromatography and gas chromatography-mass spectrometry, respectively. After degradation for 8 h, the degradation rate of saturates C10-C40 was 50.4%, while the values for short, mid and long-chain saturates were 52.6%, 49.4% and 47.7%, respectively. Biodegradation assessment markers-pristane and phytane, were degraded by 49.3% and 44.9%, respectively. The degradation rate of aromatics was 29.5%. For 2, 3, 4 and 5-ring PAHs, the corresponding values were 47.8%, 24.2%, 29.5% and 19.8%, respectively. Source tracing experiment showed that Providencia rettgeri L1 was more dominant in enriched bacterial suspensions than in petroleum environment, indicating its advantage of rapid proliferation in culture media. This study can provide some insights into fast degradation of petroleum.

The present study aimed to comprehensively dissect the petroleum hydrocarbon degradation mechanism of Acinetobacter vivianii KJ-1. The isolated and identified strain was able to proliferate using diesel as the sole carbonaceous substrate. Via comparative genomics, an in-depth analysis was performed to elucidate the genome similarities and disparities between this strain and related strains, thereby uncovering a core genome as well as genes with uncharacterized functions. Transcriptome analysis, carried out under different substrate conditions (C16, diesel, sodium acetate) manifested distinct gene expression modalities. A multitude of genes associated with alkane metabolism were differentially expressed, among which alkB1_1 and alkB1_2 was conspicuously upregulated. Prokaryotic expression of alkB1_1 was implemented, and the enzyme activity of the recombinant protein peaked at a pH level of approximately 7.0 and within a temperature range of 30 to 40 °C. The recombinant strain was shown to possess the ability to degrade n-hexadecane. Collectively, this research not only augments the understanding of the degradation mechanism of A. vivianii KJ-1 but also provides a fundamental basis for developing bioremediation strategies targeting petroleum hydrocarbon-contaminated environments.

Bioremediation is a low-cost, eco-friendly technique to reduce and/or eliminate pollutants from environment. Moreover, effective biological degrader for contaminants removal is important during bioremediation process. Here, the strain RHZ01, isolated from petroleum-contaminated soil in Shengli Oilfield, was identified as Rhodococcus qingshengii by the morphology, physiology, biochemistry and molecular biology. Strain RHZ01 was able to use diesel as the sole carbon source. The optimal initial pH and temperature for strain RHZ01 growth and diesel degradation were 6-8.5 and 20-30ºC, respectively. Nutrients (NaNO3, NH4Cl, KNO3 and Urea) could replace NH4NO3. And Mg2+ was required for strain RHZ01 growth and diesel degradation. To investigate the diesel degrading mechanisms of this strain, the complete genome was sequenced and annotated. The complete genome consists of one chromosome with a total length 6,506,318 bp and a G+C content of 62.48%. Five putative alkane monooxygenases (AlkB) encoding genes were further analyzed, and their protein sequences were characterized and compared with other published AlkBs in Rhodococcus spp.. The physicochemical features of the five AlkBs were analyzed, and these monooxygenase proteins are alkaline, unstable and thermostable. AlkB1, AlkB2 and AlkB3 are hydrophilic protein while the other proteins were hydrophobic. All of these alkane monooxygenases share several conserved regions, such as HYG-motif and three Hist boxes. From the results, it is demonstrated that bacterial strain isolated from petroleum-contaminated could be the potential bioremediation agent for diesel removal.